1. Field of the Invention
The present invention relates to a wireless communication system and, more particularly, to a wireless communication system which is suitable for a situation in which a data processing apparatus preforming wireless communication is shared by a plurality of users.
As an example of such an application, there is a situation in which a wireless keyboard is used in a wide range (angle) with respect to a personal computer which communicates with the wireless keyboard. Additionally, there is a situation in which communication between a television or video conference terminal unit and operation of a keypad is performed by wireless communication, and the keypad is used in a wide range (angle) with respect of the video conference terminal unit.
2. Description of the Related Art
When communication between a data processing apparatus and a peripheral device thereof is achieved by wireless communication, available method include radio frequency and infrared frequency transmission. Since the method using infrared transmission is achieved by a simple circuit as compared to the method using radio frequency, product cost can be reduced. Additionally, the method using infrared communication has an advantage in that power consumption is low. Accordingly, the method using an infrared is widely used, for example, in a remote control system of a television set.
In the infrared communication field, each manufacturer used a different transmission system until the Infrared Data Association, which was founded in July, 1993, standardized the IrDA system which is a standard system of the infrared data communication. The IrDA system has become popular mainly as an application for a wireless communication system between a personal computer and a peripheral device since the IrDA system can be constructed by inexpensive hardware such as a modulation and demodulation circuit, a light emitting element and a light receiving element.
The maximum communicable distance of the IrDA system is 1 meter, and 3 meters as an option. An angle range of the emitted light is .+-.15 degrees to .+-.30 degrees. The receivable angle range is more than .+-.15 degrees.
In recent years, a personal computer video conference system has become popular in which an application is shared by a remote personal computers via a communication line and transmission of audio data and video image data is performed between the remote terminals. The personal computer video conference system may be shared by a plurality of people who are attending the conference. In such a case, an operational device such as a keyboard or a drawing input device is shared by the plurality of attendants. When a plurality of attendants use the operational device in turn, it may be requested to move the operational device to a position in front of the attendant who will be using the device. At this time, if the operational device is connected by a connection cable to the personal computer, there is a disadvantage in that the attendants feel an inconvenience to draw the connection cable when moving the operational device.
Such an inconvenience may be eliminated by removing the connection cable and providing an infrared communication system according to the IrDA system instead.
Japanese Laid-Open Patent Application No. 4-55992 discloses a data collection method by a handy terminal in which a personal computer collects data from the handy terminal by using infrared communication.
Additionally, Japanese Laid-Open Patent Application No. 7-67093 discloses a video conference apparatus and a control apparatus provided with a wireless communication function in which wireless communication is provided between a terminal device and peripheral devices so that each of the peripheral devices can be operated by an operational panel of the terminal device.
As mentioned above, if the connection cable is removed and the infrared communication system is provided instead, the inconvenience caused by drawing the connection cable can be eliminated. However, there is a restriction with respect to an angular position of the operational device relative to a light emitting part of the personal computer by an angle range of an emitted light. That is, there is a problem in that the operational device cannot be used outside of the a range of emission of an infrared emitted from the personal computer. For example, when the personal computer video conference system is shared by three people, the people located on each side must pay attention to a position of the operational device when it is used. Thus, there is a problem in that efficient operation of the device is deteriorated.
In the method disclosed in the above-mentioned Japanese Laid-Open Patent Application No. 4-55992, since the data transmission by infrared communication is a one way transmission similar to the remote control system used by a television set, bidirectional communication cannot be performed. Thus, a high-quality data communication such as one having an error correction function cannot be achieved.
The forgoing document discloses that "since a receiver provided to the information processing apparatus such as a personal computer performs a crash control of data when infrared signals are simultaneously transmitted by a plurality of handy terminals, and the outputs the data to an RS232C interface after arranging the data, the data from a plurality of handy terminals can be received by a single receiver". However, a specific method of the crash control of data is not provided and, thus, it is not guaranteed that discarding of data does not occur.
In the apparatus disclosed in the above-mentioned Japanese Laid-Open Patent Application No. 7-67093, transmission of information between a digitized tablet or a microphone used by the attendant and the video conference apparatus is performed by optical communication such as infrared communication. However, the digitizer tablet or the microphone is connected to the optical communication unit by a connection cord. Thus, when the peripheral device positioned in front of the attendant is moved, there is a problem in that the attendant may feel an inconvenience to move the connection cord.